This invention relates to heating, ventilating and air conditioning systems, and more particularly, to an air mixing apparatus of simplified construction which still achieves adequate mixing efficiency while maintaining a uniform velocity profile and minimum pressure drop.
Air streams which are introduced at different temperature levels through a common duct in heating, ventilating and air conditioning (HVAC) systems require intimate mixing in the duct in order to avoid undesirable stratification of air prior to passage of the airstream into a room airspace to be heated or cooled. Failure to achieve intimate mixing in the duct ultimately results in inefficient heating and cooling of the room air space and therefore can significantly affect the cost in operating and maintaining an HVAC system.
A number of prior art references exist which disclose various static air mixing devices. The assignee of the current invention is the owner of a number of previous patents to include U.S. Pat. Nos. 3,180,245; 4,495,858; 5,645,481; and 5,536,207. Each of these references are hereby incorporated by reference for teaching the basic air mixing apparatuses disclosed therein.
An air mixing device installed in an air duct inherently creates a pressure drop in the airflow across the air mixer during operation. This pressure drop is undesirable and therefore, efforts to minimize pressure drop is a main consideration in static air mixing design. Of course, it is also desirable to maximize the efficiency of the mixing that takes place immediately downstream of the mixing apparatus as well as to maintain a uniform velocity profile downstream of the mixing device.
Earlier mixer designs typically had mixing efficiencies of around 30%. In later mixer designs, mixing effectiveness has been greatly improved, and it is not uncommon to find mixers with efficiencies of around 50 or 60%. With the optimized construction of the air mixers disclosed in the U.S. Pat. Nos. 5,645,481 and 5,536,207, air mixing effectiveness of at least 65% was achieved.
Although mixing efficiency has improved due to newer mixer designs, one drawback from some of the newer mixer designs is the complexity of the air mixers, and the cost to manufacture such units.
Therefore, there is a need for development of yet a different mixer design which still achieves acceptable mixer effectiveness, but is of a simpler design which reduces manufacturing costs and makes the mixer more available for all types of commercial use.
It is therefore an object of the present invention to provide an improved static air mixing apparatus which still achieves acceptable mixing effectiveness; however, the design of the mixer is simplified to reduce manufacturing costs.
Other objects of the invention include, but are not limited to, providing a static air mixing apparatus which still maintains a minimum pressure drop, yet is able to maintain a uniform downstream velocity profile.
In accordance with the present invention, a static air mixing apparatus is provided which meets the aforementioned needs. As with the previous static air mixing apparatuses of the assignee, the current static air mixing apparatus is installed within a duct wherein an enclosure partially traverses the duct defining a core area therein. A plurality of radially extending curved vanes are centered within the enclosure, and the vanes diverge away from a center of the enclosure and terminate at their outer distal ends at or adjacent to the inner wall of the enclosure. The vanes can be defined as including an inner section wherein the vane curves downstream in a first direction, and an outer section which lies radially outward from the inner section; however, the outer section curves downstream in a second direction away from the first section. An interface can be defined as the location at which the distal end of the inner section abuts the proximal end of the outer section. At this interface, the vane is split into its oppositely arranged curved sections.
It is also contemplated within the current invention that yet another section of the vane can be provided which is curved in yet a third direction downstream, different than first and second directions of the inner and outer sections.
Although each vane has been defined as having an inner and outer section, the invention can also be thought of as including a plurality of inner vanes and outer vanes wherein an inner vane and a corresponding outer vane share a common leading edge, but have divergent trailing edges.
In comparison to the apparatuses disclosed in U.S. Pat. Nos. 5,645,481 and 5,136,207, the air mixer of the present invention has slightly less mixing efficiency; however, the construction of the present invention is greatly simplified which reduces manufacturing costs. Furthermore, the mixing method of the present invention greatly differs from the previous inventions of the assignee as further explained below. A comparison of the turbulence created by the present mixer design clearly shows the structural differences in the present invention also results in different air mixing dynamics.